>Assuming of course that you have competent and trustworthy managers.

You're begging the question.

"Competent and trustworthy" people won't abuse their power by definition. Anyone who abuses their power intentionally is untrustworthy, and anyone who abuses their power unintentionally is incompetent.

In the real world there are many incompetent and untrustworthy leaders. Slack has no choice but to operate in the real world.